Compact lumped element dual highpass/lowpass balun layout

ABSTRACT

A circuit layout for a lumped element dual-balun ( 248 ) where the elements of the dual-balun ( 248 ) are patterned on a monolithic substrate ( 250 ) in a compact design. The dual-balun ( 248 ) includes four inductors ( 252, 254, 256, 258 ) and four capacitors ( 340, 342, 360, 388 ) electrically coupled together to provide two zero phase RF output signals and two 180° phase RF output signals. The inductors ( 252, 254, 256, 258 ) are symmetrically disposed in a rectangular area on the substrate ( 250 ). A first pair of the inductors ( 252, 254 ) is positioned at one end of the rectangular area, and a second pair of the inductors ( 256, 258 ) is positioned at an opposite end of the rectangular area. The capacitors ( 340, 342, 360, 388 ) are formed on the monolithic substrate ( 250 ) in a central circuit area ( 260 ) between the first pair ( 252, 254 ) and the second pair of inductors ( 256, 258 ). RF output lines ( 350, 354, 372, 390 ) are coupled to circuit elements in the circuit area ( 260 ) and extend out of the circuit area ( 260 ) between the first a pair and the second pair of the inductors ( 252, 254, 256, 258 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a lumped element dual-balun and,more particularly, to a circuit layout for a lumped element dual-balunfor a star mixer or a double doubly balanced mixer, where the balunelements are configured on a monolithic substrate so that capacitiveelements are disposed in a channel area defined between symmetricallydisposed inductive elements.

2. Discussion of the Related Art

Modern communications systems employ transmitter and receiver designsthat attempt to maximize the utilization of the assigned frequencybandwidth associated with the various communications channels becausesignal bandwidth is a costly investment for the system provider.Maximizing the utilization of the assigned bandwidth translates toproviding transmitters and receivers that have extremely highperformance. However, the transmitters and receivers must also be lowcost. The radio frequency (RF) components in a communications systemtypically are the highest cost items because they are usually customdesigned elements and are not mass produced.

One RF component that falls into this category is a frequency mixer. Afrequency mixer mixes two RF or intermediated frequency (IF) signals tocreate a sum and difference frequency for frequency down-conversion orfrequency up-conversion purposes. For example, the signal received inthe receiver is mixed with a local oscillator (LO) signal to generate anIF signal suitable for subsequent signal processing. Typically, mixersare critical for setting the performance of the RF signal chain. Thus,mixers with lower intermodulation products and high dynamic range thatcan be implemented as a cell in an RF integrated circuit (IC) areneeded.

One known mixer employed in RF communications systems of the type beingdiscussed herein is referred to in the art as a ring mixer. A ring mixeremploys four diodes connected in a ring configuration that mix the RFsignal and the LO signal to generate the IF signal. The ring mixeremploys a hybrid or balun that splits the RF signal and the LO signalinto signals that are 180° out of phase with each other. A ring mixerbalun is disclosed in Sturdivant, Rick, “Balun Designs for Wireless, . .. Mixers, Amplifiers and Antennas,” Applied Microwave, Summer 1993, pps.34-44. The split RF signals and the LO signals are applied to the mixerbetween the diodes at opposite corners of the ring. The diodes areswitched on and off in response to the positive and negative portions ofthe RF signals to provide modulation. The IF signal is generated betweenthe diodes at the other opposite corners of the ring.

FIG. 1 is a schematic diagram of a known lumped element ring baluncircuit 10. The ring balun circuit 10 includes an electrical ring 12having four sides defining corner nodes 14, 16, 18 and 20. The ringbalun circuit 10 includes an electrical configuration of capacitorsC₁-C₆, inductors L₁-L₄ and a resistor R₁. Each side of the ring 12includes a capacitor and an inductor that combine to provide a high passfilter that forms a lumped element transmission line that causes a delayof a signal propagating therethrough. As is known in the art, currentleads voltage on a capacitor, and voltage leads current on an inductor.Therefore, a series capacitor and shunt inductor provide a phase lead ofthe signal, and a series inductor and a shunt capacitor provide a phaselag of the signal.

An RF input signal is applied to the node 14, and the filters provide anRF signal at the node 20 that is 90° out of phase with the signal at thenode 14, an RF signal at the node 18 that is 180° out of phase with thesignal at the node 14, and an RF signal at the node 16 that is 270° outof phase with the signal at the node 14. Output lines 54 and 56 arecoupled to the nodes 20 and 16, respectively, to provide output signalsthat are 180° out of phase with each other. DC blocking capacitors 24and 26 are provided in the output lines 54 and 56 to prevent DC signalsfrom the mixer from entering the ring balun circuit 10.

The ring balun circuit 10 is applicable for a ring mixer, but is limitedin use for other types of mixers, such as star mixers and double doublybalanced mixers, because of the complexities in providing a dual balunin the ring design. Therefore, other balun designs are employed in theart for other types of mixers. FIG. 2 is a schematic diagram of a lumpedelement dual-balun circuit 30 including a first balun 32 and a secondbalun 34 that has particular application for use in combination with astar mixer or a monolithic microwave integrated circuit (MMIC) doubledoubly balanced mixer (DDBM). The dual-balun circuit 30 receives an RFinput signal, and the first balun 32 outputs two signals that are 180°out of phase with each other and the second balun 34 outputs two RFsignals that are 180° out of phase with each other. A dual-balunstructure of this type is disclosed in Chiou, Hwann-Keo, et al.,“Miniature MMIC Star Double Balanced Mixer Using Lumped Dual Balun,”Electronics Letters, Vol. 33, No. 6, Mar. 13, 1997, pps. 503-505, andChiou, Hwann-Keo, et al., “A Miniature MMIC Double Doubly Balanced MixerUsing Lumped Dual Balun for High Dynamic Receiver Application,” IEEE,Microwave and Guided Wave Letters, Vol. 7, No. 8, August 1997, pps.227-229.

The dual-balun circuit 30 employs inductor and capacitor filter networksin the same manner as the balun circuit 10 discussed above to providethe RF signals that are 180° out of phase with each other. The balun 32includes a filter made up of inductor L₁ and capacitor C₁ and a filtermade up of inductor L₂ and capacitor C₂. Likewise, the balun 34 includesa filter made up of inductor L₃ and capacitor C₃ and a filter made up ofinductor L₄ and capacitor C₄. In the balun 32, the inductor L₁ iscoupled to the capacitor C₁ at node 36, the inductor L₁ is coupled tothe capacitor C₂ at node 38, the capacitor C₂ is coupled to the inductorL₂ at node 40, and the inductor L₂ is coupled to the capacitor C₁ atnode 42. In the balun 34, the inductor L₃ is coupled to the capacitor C₃at node 44, the inductor L₃ is coupled to the capacitor C₄ at node 46,the capacitor C₄ is coupled to the inductor L₄ at node 48, and theinductor L₄ is coupled to the inductor C₃ at node 50. The RF inputsignal is applied to the nodes 36 and 44. An RF output signal that is inphase with the RF input signal is provided at the nodes 42 and 50, andan RF output signal that is 180° out of phase with the RF input signalis provided at the nodes 38 and 46.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, a circuitlayout for a lumped element dual-balun is disclosed where the elementsof the dual-balun are patterned on a monolithic substrate in a compactdesign. The dual-balun includes four inductors and four capacitorselectrically coupled together to filter and delay an RF input signal toprovide two zero phase RF output signals and two 180° phase RF outputsignals. The inductors are symmetrically disposed in a rectangular areaon the substrate. A first pair of the inductors is positioned at one endof the rectangular area, where the inductors are adjacent to each other,and a second pair of the inductors is positioned at an opposite end ofthe rectangular area, where the inductors are adjacent to each other.All of the capacitors are formed on the substrate in a central circuitarea between the first pair of inductors and the second pair ofinductors.

The design employs metallized traces patterned on the substrate toprovide electrical coupling between the inductors and the capacitors.Each inductor includes a winding having an inner end and an outer endthat are electrically coupled to circuit elements in the circuit area.The inner end of each winding is coupled to a trace that extends underthe winding through an air bridge to be electrically isolated thereform.The four RF output lines are coupled to circuit elements at a centrallocation of the circuit area and extend out of the circuit area betweenthe first pair of inductors and the second pair of the inductors in aparallel manner.

Additional objects, advantages and features of the present inventionwill become apparent from the following description and appended claims,taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a known ring balun for a ring mixer;

FIG. 2 is a schematic diagram of a known dual-balun for a star mixer ora double doubly balanced mixer;

FIG. 3 is a top view of a layout on a monolithic substrate for theelements of a ring balun of the type shown in FIG. 1, according to anembodiment of the present invention; and

FIG. 4 is a top view of a layout on a monolithic substrate for theelements of a dual-balun of the type shown in FIG. 2, according toanother embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following discussion of the invention directed to a specializedcircuit layout for a balun on a monolithic substrate is merely exemplaryin nature, and is in no way intended to limit the invention or itsapplications or uses.

The present invention proposes an arrangement of the inductive andcapacitive elements of the balun circuit 10 and the dual-balun circuit30 on a monolithic substrate that conserves space, reduces parasiticcapacitances and inductances, uses less power and is low cost. The baluncircuit 10 is intended to be used in connection with a ring mixer andthe dual-balun circuit 30 is intended to be used in connection with astar mixer or a DDBM. However, this is by way of a non-limiting examplein that the balun configuration of the invention discussed below willhave application to other systems including other mixers, amplifiers,antennas, etc. Further, the present invention can be configured toprovide other phase shifts in signals other than 180° phase shifts.Also, the layout design can be employed in other types of circuits, suchas integrated circuits on an integrated circuit board.

FIG. 3 is a top view of a circuit layout for a ring balun 60 thatincludes the same electrical elements as the balun circuit 10 discussedabove. The electrical elements are patterned on a monolithic substrate62, such as an MMIC, by any suitable metalization and deposition processthat provides conductive and dielelectric areas to define the elements.The substrate 62 can be any suitable material, such as InP, GaAs,sapphire, etc. Rectangular areas in the traces and metalized regionsdiscussed below represent vertically extending or overlapping metalareas to provide the electrical coupling. Many techniques are known forpatterning inductors as metallized traces or windings on a monolithicsubstrate and for patterning capacitors as metallized patches havingopposing plates and a dielectric formed therebetween. The invention goesto the orientation of the inductors and capacitors on the substrate 62.In this regard, the various electrical elements of the balun 60 will bediscussed with reference to the schematic representation of thoseelements as shown in FIG. 1.

The balun 60 includes symmetrically disposed inductors including a firstinductor 64, representing the inductor L₁, a second inductor 66,representing the inductor L₂, a third inductor 68, representing theinductor L₃, and a fourth inductor 70, representing the inductor L₄. Aswill be discussed below, the various capacitors C₁-C₆ and theinterconnection between the capacitors C₁-C₆ and the inductors L₁-L₄ areprovided in a central circuit area 72 defined between the pair of theinductors 64 and 66 and the pair of the inductors 68 and 70. Bysymmetrically disposing the inductors 64-70 on the substrate 62 in thismanner, and confining the other circuit elements to a central locationtherebetween, significant advantages are provided for limiting the spacerequirements of the balun 60.

The inductor 64 includes a metallized trace defining a winding 74 havingan inner end 76 and an outer end 78. The inductor 66 includes ametallized trace defining a winding 90 having an inner end 92 and anouter end 94. The inductor 68 includes a metallized trace defining awinding 96 having an inner end 98 and an outer end 100. The inductor 70includes a metallized trace defining a winding 104 having an inner end106 and an outer end 108. Although the inductors 64-70 are shown in arectangular orientation, other designs consistent with the scope of thepresent invention can include other shapes, including hexagonal,circular, elliptical, etc.

Each of the inner ends 76, 92, 98 and 106 is electrically coupled tocircuit elements in the circuit area 72. To provide this electricalcoupling with the necessary electrical isolation, an air bridge isformed beneath a portion of the windings 74, 90, 96 and 104. Theairbridges are formed by a raised portion of the winding so that thewinding does not electrically connect with the trace and has minimalelectrical coupling thereto. An interconnect via as discussed herein isa metallized region for electrically connecting two traces, or anoverlap region of two traces.

The end 76 of the winding 74 is electrically coupled to a metal trace120 by an interconnect via 122. The trace 120 extends through an airbridge 124 formed by the winding 74 to be electrically isolatedtherefrom, and is coupled to a metallized region 130 by an interconnectvia 128, where the region 130 defines the node 14. The end 92 of thewinding 90 is electrically coupled to a metal trace 136 by aninterconnect via 138. The trace 136 extends through an air bridge 140formed by the winding 90 to be electrically isolated therefrom, and iscoupled to a metallized region 144 by an interconnect via 142, where theregion 144 defines the node 18. The end 98 of the winding 96 iselectrically coupled to a metal trace 150 by an interconnect via 152.The trace 150 extends through an air bridge 154 formed by the winding 96to be electrically isolated therefrom, and is coupled to a metallizedregion 158 by an interconnect via 156, where the region 158 alsorepresents the node 18. The end 106 of the winding 104 is electricallycoupled to a metal trace 170 by an interconnect via 172. The trace 170extends through an air bridge 174 formed by the winding 104 to beelectrically isolated therefrom, and is coupled to a metallized region182 by a via 176.

A top plate of a capacitor 190, representing the capacitor C₁, iselectrically coupled to the metallized region 130, and a bottom plate ofthe capacitor 190 is coupled to a ground via 180. The via 180 extendsthrough the substrate 62 and is electrically coupled to a metallizedground plane (not shown) on an opposite surface of the substrate 62. Thevia 180 is electrically coupled to a metallized region 178 that acts asa ground patch on the top surface of the monolithic substrate 62. Themetallized region 178 is electrically coupled to the metallized region182 so that the end 106 of the winding 104 is coupled to ground.

A top plate of a capacitor 192, representing the capacitor C₆, iselectrically coupled to the metallized region 130 so that the inductor64 and the capacitor 192 are electrically coupled. A bottom plate of thecapacitor 192 is electrically coupled to a metallized region 194representing the node 22. A top plate of a capacitor 198, representingthe capacitor C₅, is electrically coupled to the metallized region 194and is electrically coupled to the end 108 of the winding 104. A bottomplate of the capacitor 198 is electrically coupled to the end 100 of thewinding 96 and is electrically coupled to a metallized region 200,representing the node 20. A top plate of a capacitor 202, representingthe capacitor C₄, is electrically coupled to the metallized region 200,and a bottom plate of the capacitor 202 is electrically coupled to ametallized region 206. A bottom plate of a capacitor 226, representingthe capacitor C₂, is also electrically coupled to the metallized region206. A top plate of the capacitor 226 is electrically coupled to the end78 of the winding 74 and the end 94 of the winding 90. This connectionpoint represents the node 16.

A metallized region 210 on a top surface of the monolithic substrate 62is electrically coupled to a ground via 208 that is electrically coupledto the ground plane. The metallized region 206 is also electricallycoupled to the via 208. A bottom plate of a capacitor 214, representingthe capacitor C₃, is electrically coupled to the metallized region 210.A top plate of the capacitor 214 is electrically coupled to themetallized regions 144 and 158 to couple the inductors 66 and 68 to thecapacitor 214. The top plate of the capacitor 214 is also coupled to ametallized region 216, representing the resistor R₁. The metallizedregion 216 is also coupled to a metallized region 218 that iselectrically coupled to a ground via 220. The via 220 extends throughthe monolithic substrate 62 and is electrically coupled to the groundplane.

The RF input signal, applied to the node 14, is applied to a metallizedregion 230. The metallized region 230 is electrically coupled to the topplate of the capacitor 190. A 180° phase output trace 232 iselectrically coupled to the top plate of the capacitor 226, and extendsbetween the inductors 64 and 66, as shown. A DC blocking capacitor 234,representing the capacitor 24, is coupled to the output trace 232. Azero phase output trace 236 is electrically coupled to the top plate ofthe capacitor 198, and extends between the inductors 68 and 70, asshown. A DC blocking capacitor 238 is coupled to the output trace 236.

FIG. 4 is a top view of a circuit layout for a dual-balun 248 thatincludes the same elements as the dual-balun circuit 30 shown in FIG. 2.The elements of the dual-balun 248 are formed on a monolithic substrate250. The dual-balun 248 includes a first inductor 252, representing theinductor L₁, a second inductor 254, representing the inductor L₂, athird inductor 256, representing the inductor L₃, and a fourth inductor258, representing the inductor L₄. As will be discussed below, thevarious capacitors C₁-C₄ and the interconnection between the capacitorsC₁-C₄ and the inductors L₁-L₄ are provided in a central circuit area 260defined between the pair of the inductors 252 and 254 and the pair ofthe inductors 256 and 258.

The inductor 252 includes a metallized trace defining a winding 262having an inner end 264 and an outer end 266. The inner end 264 iselectrically coupled to a metal trace 268 by an interconnect via 270.The trace 268 extends through an air bridge 274 formed by the winding262 and is electrically coupled to an interconnect via 276. The via 276is electrically coupled to a metallized region 278 that represents thenode 36.

The inductor 254 includes a metallized trace defining a winding 282having an inner end 284 and an outer end 286. The inner end 284 iselectrically coupled to a metal trace, 288 by an interconnect via 290.The trace 288 extends through an air bridge 292 formed by the winding282 and is electrically coupled to an interconnect via 294. The via 294is electrically coupled to a metallized region 296 that represents thenode 40.

The inductor 256 includes a metallized trace defining a winding 300having an inner end 302 and an outer end 304. The inner end 302 iselectrically coupled to a metal trace 306 by an interconnect via 308.The trace 306 extends through an air bridge 310 formed by the winding300 and is electrically coupled to an interconnect via 312. The via 312is electrically coupled to a metallized region 314 that represents thenode 44.

The inductor 258 includes a metallized trace defining a winding 320having an inner end 322 and an outer end 324. The inner end 322 iselectrically coupled to a metal trace 326 by an interconnect via 328.The trace 326 extends through an air bridge 330 formed by the winding320 and is electrically coupled to an interconnect via 332. The via 332is electrically coupled to a metallized region 334 that represents thenode 48.

A top plate of a capacitor 340, representing the capacitor C₁, iselectrically coupled to the metallized region 278 so that the capacitor340 is electrically coupled to the inductor 252. Likewise, a top plateof a capacitor 342 is electrically coupled to the metallized region 314so that the capacitor 342 is electrically coupled to the inductor 256. Ametallized region 344 is coupled to the metallized regions 278 and 314,and represents an input port for receiving the input RF signal. Thus,the input RF signal is applied to the capacitors 340 and 342 and theinductors 252 and 256 in the same manner as the input signal for thedual-balun circuit 30.

A bottom plate of the capacitor 340 is electrically coupled to ametallized region 348, representing the node 42, that is electricallycoupled to a zero phase output line 350. The outer end 286 of thewinding 282 is also coupled to the output line 350. Likewise, a bottomplate of the capacitor 342 is electrically coupled to a metallizedregion 352, representing the node 50, that is electrically coupled to azero phase output line 354. The outer end 324 of the winding 320 is alsocoupled to the output line 354.

A bottom plate of a capacitor 360, representing the capacitor C₂, iselectrically coupled to the metallized region 296. The metallized region296 is electrically coupled to a metallized region 362 that iselectrically coupled to a ground via 364. The ground via 364 extendsthrough the substrate 250 and is electrically coupled to a ground plane(not shown) on an opposite surface of the substrate 250. Therefore, theinductor 254 and the capacitor 360 are electrically coupled to ground. Atop plate of the capacitor 360 is electrically coupled to a metallizedregion 370. The end 266 of the winding 262 and the metallized region 370are electrically coupled to a 180° phase output trace 372 so that theinductor 254 and the capacitor 360 are coupled thereto. A dielectricregion 374 electrically isolates the output traces 350 and 372.

A bottom plate of a capacitor 380, representing the capacitor C₄, iselectrically coupled to the metallized region 334. The metallized region334 is electrically coupled to a metallized region 382 that iselectrically coupled to a ground via 384. The ground via 384 iselectrically coupled to the ground plane so that the inductor 258 andthe capacitor 380 are coupled to ground. A top plate of the capacitor380 is electrically coupled to a metallized region 386. The end 304 ofthe winding 300 and the metallized region 386 are electrically coupledto a 180° phase output line 390 so that the inductor 256 and thecapacitor 380 are coupled thereto. A dielectric region 392 isolates theoutput traces 354 and 390.

The symmetrical design of the dual-balun 248 allows the output traces350, 354, 372 and 390 to extend parallel to each other through thecircuit area 260 between the inductors 254 and 258. This design providessignificant advantages for balun performance in a compact design.Further, by minimizing the size and length of the various metallizedregions that couple circuit elements to the capacitors, parasiticinductances on the capacitors are minimized.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. One skilled in the art willreadily recognize from such discussion and from the accompanyingdrawings and claims, that various changes, modifications and variationscan be made therein without departing from the spirit and scope of theinvention as defined in the following claims.

What is claimed is:
 1. A dual-balun formed on a substrate, saiddual-balun comprising: four inductors symmetrically disposed in arectangular area on the substrate, each inductor including an electricalwinding having a first end and a second end, wherein a first inductorand a second inductor are positioned adjacent to each other at one sideof the rectangular area and a third inductor and a fourth inductor arepositioned adjacent to each other at an opposite side of the rectangulararea so that a circuit area including circuit elements is definedbetween the pair of the first and second inductors and the pair of thethird and fourth inductors in a central portion of the rectangular area;and a first output trace electrically coupled to the first end of thefirst inductor in the circuit area, a second output trace electricallycoupled to the first end of the second inductor in the circuit area, athird output trace electrically coupled to the first end of the thirdinductor in the circuit area and a fourth output trace electricallycoupled to the first end of the fourth inductor in the circuit area,wherein the first, second, third and fourth output traces extend throughthe circuit area between the second and fourth inductors, and wherein anoutput signal on the first output trace is out of phase with an outputsignal on the second output trace and an output signal on the thirdoutput trace is out of phase with an output signal on the fourth outputtrace.
 2. The dual-balun according to claim 1 wherein the first end ofeach winding is an outer end of the winding and the second end of eachwinding is an inner end of the winding.
 3. The dual-balun according toclaim 2 wherein the inner end of each winding is-electrically coupled toa circuit element in the circuit area by an air bridge formed byparallel portions of the winding of the inductor.
 4. The dual-balunaccording to claim 2 wherein the inner end of each winding iselectrically coupled to a capacitor in the circuit area.
 5. Thedual-balun according to claim 2 wherein the inner ends of the windingsof the first and third inductors are coupled to an RF input metallizedregion, and the inner ends of the windings of the second and fourthinductors are coupled to a ground via.
 6. The dual-balun according toclaim 1 wherein the circuit elements include a plurality of capacitorsin the circuit area, wherein the inductors and the capacitors areelectrically coupled together to define the lumped element dual-balun.7. The dual-balun according to claim 6 wherein the plurality ofcapacitors is four capacitors.
 8. The dual-balun according to claim 1wherein the circuit elements are selected from the group consisting ofground vias and capacitors.
 9. The dual-balun according to claim 6wherein at least one of the capacitors includes three plates.
 10. Thedual-balun according to claim 1 wherein the dual-balun is a lumpedelement star mixer balun.
 11. A dual-balun for providing two zero phaseRF output signals and two 180° phase RF output signals, said dual-baluncomprising: a monolithic substrate; four inductors symmetricallydisposed on the substrate, each inductor including an electrical windinghaving an inner end and an outer end, wherein the inductors include apair of a first inductor and a second inductor where the first andsecond inductors are positioned adjacent to each other and a pair of athird inductor and a fourth inductor where the third and fourthinductors are positioned adjacent to each other, wherein a circuit areais defined between the pair of the first and second inductors and thepair of the third and fourth inductors; and four capacitors disposed inthe circuit area, wherein the inner end of each winding is electricallycoupled to a capacitor in the circuit area by an air bridge formed byparallel portions of the winding of the inductor, and wherein the innerend of the first end inductor is electrically coupled to a firstcapacitor, the inner end of the second inductor is electrically coupledto a second capacitor, the inner end of the third inductor iselectrically coupled to a third capacitor and the inner end of thefourth inductor is electrically coupled to a fourth capacitor.
 12. Thedual-balun according to claim 11 further comprising a first output traceelectrically coupled to the outer end of the winding of the firstinductor in the circuit area, a second output trace electrically coupledto the outer end of the winding of the second inductor in the circuitarea, a third output trace electrically coupled to the outer end of thewinding of the third inductor in the circuit area and a fourth outputtrace electrically coupled to the outer end of the winding of the fourthinductor in the circuit area, and wherein an output signal on the firstoutput trace is 180° out of phase with an output signal on the secondoutput trace and an output signal on the third output trace is 180° outof phase with an output signal on the fourth output trace.
 13. Thedual-balun according to claim 12 wherein the first, second, third andfourth output traces are parallel to each other and extend through thecircuit area between the second and fourth inductors.
 14. The dual-balunaccording to claim 11 wherein the inner ends of the windings of thefirst and third inductors are coupled to an RF input metallized region,and the inner ends of the windings of the second and fourth inductorsare coupled to a ground via.
 15. The dual-balun according to claim 11wherein at least one of the capacitors includes three plates.
 16. Thedual-balun according to claim 11 wherein the dual-balun is a lumpedelement star mixer balun.
 17. A dual-balun for providing two zero phaseRF output signals and two 180° phase RF output signals for a mixer, saiddual-balun comprising: a monolithic substrate; four inductorssymmetrically disposed on the substrate, each inductor including anelectrical winding having an inner end and an outer end, wherein theinductors include a pair of a first inductor and a second inductor wherethe first and second inductors are positioned adjacent to each other anda pair of a third inductor and a fourth inductor, where the third andfourth inductors are positioned adjacent to each other, wherein acircuit area is defined between the pair of the first and secondinductors and the pair of the third and fourth inductors; fourcapacitors disposed in the circuit area, wherein the inner end of eachwinding is electrically coupled to a capacitor in the circuit area by anair bridge formed by parallel portions of the winding of the inductor;and a first output trace electrically coupled to the outer end of thewinding first inductor in the circuit area, a second output traceelectrically coupled to the outer end of the winding of the secondinductor in the circuit area, a third output trace electrically coupledto the outer end of the winding of the third inductor in the circuitarea and a fourth output trace electrically coupled to the outer end ofthe winding of the fourth inductor in the circuit area, and wherein anoutput signal on the first output trace is 180° out of phase with anoutput signal on the second output trace and an output signal on thethird output trace is 180° out of phase with an output signal on thefourth output trace, and wherein the first, second, third and fourthoutput traces are parallel to each other and extend through the circuitarea between the second and fourth inductors.
 18. The dual-balunaccording to claim 17 wherein the mixer is selected from the groupconsisting of star mixers and double doubly balanced mixers.
 19. Thedual-balun according to claim 17 wherein the inner ends of the windingsof the first and third inductors are coupled to an RF input metallizedregion, and the inner ends of the windings of the second and fourthinductors are coupled to a ground via.